The invention relates to composite materials for structural members used in commercial and residential architecture and specifically in the manufacture or fabrication of fenestration units such as windows and doors. The composite is made using an extrusion process with an input of polyolefin and wood fiber to form a composite material having improved properties. The materials have improved processability, thermal and structural properties when compared to metal, vinyl, or wooden components and when compared to other polymeric or polyolefin composites. The structural members of the invention can be used in the form of elements used in institutional and residential construction such as framing members, beams, sized lumber, trim, siding, shingle, jambs, stiles, sills, tracks, sash and other components. These applications can require a low cost, complex, thin-walled, hollow profile structural member. The composite can be made with intentional recycle of by-product or waste streams comprising components used in the manufacture of the fenestration unit, if desired.
In conventional construction materials and in window and door manufacture, vinyl, vinyl composite, wood and metal components are used in forming structural members. Most commonly siding, trim, window or door units are typically made from extruded vinyl or aluminum or milled wood members. Such materials and units made of these materials, require maintenance and are often energy inefficient. Vinyl materials have been used in forming envelopes, profile and seal components in window units. Such vinyl materials typically comprise a major proportion of vinyl polymer with inorganic pigments, fillers, lubricants, etc. Extruded or injection mold of thermoplastic materials have been used, filled and unfilled as flexible and rigid thermoplastic materials used in seals, trims, fasteners, and other window construction parts. Thermoplastic polyvinylchloride has been combined with wood members in the manufacture of PERMASHIELD(copyright) brand windows manufactured by Andersen Corporation for many years. The technology is disclosed in Zaninni, U.S. Pat. Nos. 2,926,729 and 3,432,885. Generally, PVC materials is used as a cladding or coating. The PVC technology used in making PERMASHIELD(copyright) brand windows involve extruding or injection molding thin polyvinylchloride coating or envelope onto a shaped wooden structural member. One useful alternative to vinyl envelopes around wood members is a polyvinylchloride wood fiber composite such as that disclosed in patents assigned to Andersen Corporation including U.S. Pat. Nos. 5,406,768; 5,441,801; 5,486,553; 5,539,027; 5,497,594; 5,695,874; 5,518,677; 5,827,607 and published European Patent Application No. 586,212, and others.
Polyolefin materials such as polyethylene and propylene, common polyolefin compositions, have been available in a variety of grades and forms for many years. In large part, polypropylene has not been used in exterior applications or as exterior structural members due to its limited structural capacity and its inability to resist the damaging effect of weather, typically heat, light and cold. Recently, polypropylene has been used in a variety of applications in which the polypropylene is combined with a reinforcing composition in a variety of ways. For example, Shinomura, U.S. Pat. No. 3,888,810, teaches a thermoplastic composite comprising a thermoplastic resin, fibrous materials and preferably synthetic or natural rubbers. Jones, U.S. Pat. No. 3,917,901, teaches a conductor having an insulative layer comprising a polyolefin-wood composite. Nakano et al., U.S. Pat. No. 3,962,157, claim a polypropylene composition modified with a porous filler and a free radical agent that promotes reaction between the filler and the polymer. Laver, U.S. Pat. No. 5,516,472, claims an apparatus and method for making a composite which forms, internally, pellet-like strands that are then recombined to form an extruded part. Bainbridge et al., U.S. Pat. No. 5,766,395, claim a self-supporting composite structure in the form of a panel made by compression molding composite materials. The prior art also discloses a large proportion of patents that compatibilize a combination of a polyolefin with a cellulose filler using such materials as plasticizers, monomeric silicone containing compounds, grafted silyl moieties on either the polymer or the filler, polyolefin lubricants, blends of varied types of polymers in combination with the primary polyolefin, synthetic elastomers and rubbers, methylol phenolic modified polyolefins, blends of ethylene polymers and polypropylene polymers, in situ polymerization of monomers onto a fiber used in the making of a composite, specialized fibers including polytetrafluoroethylene fibers, expanded or otherwise specially modified polyolefins, glyoxal and other types of thermally reactive crosslinking agents, modified cellulosic fibers including the use of metals, crosslinking agents, compatibilizing agents, etc. Wold, U.S. Pat. No. 5,435,954, teaches a molding method for forming a composite into a usefull article.
The polypropylene art has shown significant advancement and sophistication in learning to obtain new physical properties from polypropylene, various fibers and reagents or other polymers. Representative examples of recent developments in the manufacture of polypropylene compositions, particularly metallocene catalyst manufactured propylene, is shown in the technical literature owned by Montell North America Inc. For example, Malucelli et al., U.S. Pat. No. 5,574,094, teach improved polyolefin compositions comprising one or more crystalline materials having a melt index higher than 20 grams-10 minxe2x88x921 combined with a cellulosic particle or fiber. Malucelli et al. disclose pelletizing such a composite and converting such a pellet into products by way of injection molding. Sacchetti et al., U.S. Pat. No. 5,691,264, disclose a bimetallic metallocene catalyst containing at least one M-xcfx80 bond combined with a support comprising magnesium halide in the gas phase polymerization of an olefin such as propylene into a structural polymeric product. In particular, these catalysts obtain the polymerization of olefins such as propylene into high molecular weight useful materials. The patent literature describes bimetallic catalysts comprising a compound of titanium or vanadium supported on a magnesium halide reactive with a metallocene compound containing at least one cyclopentadienyl ring coordinated on a transition metal selected from V, Ti, Zr, Hf, or mixtures thereof. Examples of such catalysts are described in U.S. Pat. No. 5,120,696, EP-A-447070 and EP-A-447071. The bimetallic catalysts can be obtained by impregnating a silica support with a magnesium compound of the type MgR2, wherein R is a hydrocarbon radical and then reacting the treated support with a compound of Ti, such as TiCl4, optionally with SiCl4 and thereafter with a metallocene compound. Such materials are shown in EP-A-514594. Such bimetallic catalysts obtained by these treatments and then with other titanocenes such as dicyclopentadienyl titanium dichloride and bis(indenyl) titanium dichloride are shown in EP-A-412750. Similar catalysts obtained by treating carbonated compounds of magnesium such as alkyl magnesium carbonate, with titanium dichloride in the presence of a metallocene compound of Hf or Zr, are known from PCT Application WO 94/03508. Bimetallic catalysts comprising a titanium based catalyst in which the Ti compound is supported on a Mg halide, a metallocene compound and a poly(methylaluminoxane) (a MAO) are disclosed in EP-A-436399. Sacchetti et al., U.S. Pat. No. 5,698,487, disclose additional compositions and methods for preparation of metallocene catalysts for preparing polyolefin materials. Govoni et al., U.S. Pat. No. 5,698,642, disclose a particular gas phase polymerization project having two interconnected polymerization zones for olefin polymerization. Sacchetti et al., U.S. Pat. No. 5,759,940, disclose further information on the preparation of catalytic materials for the manufacture of polyolefin materials. Additional details for manufacturing modern metallocene catalysts are shown in U.S. Pat. No. 4,542,199 and EP-A-129368; EP-A-185918; EP-A-485823; EP-A-485820; EP-A-51237; and U.S. Pat. Nos. 5,132,262; 5,162,278; 5,106,804. The more modern polypropylene polymeric materials show improvement in physical properties when compared to the materials made using the initially formulated Zigler-Natta catalytic materials developed since the early 1960""s.
Kourgli, U.S. Pat. No. 5,542,780, discloses a polypropylene composite having an elastic modulus of about 500,000 or less. Coran et al., U.S. Pat. No. 4,323,625, teach a polypropylene composite having 20 wt % of a hardwood pulp and a modulus less than 200,000. Nishibori, U.S. Pat. No. 5,725,939, teaches a wood meal polypropylene composite with 50% polymer and a modulus less than 400,000. Beshay, U.S. Pat. No. 4,717,742, discloses an aspen pulp polypropylene composite having 40 wt % pulp and a tensile modulus less than 100,000. Beshay, U.S. Pat. No. 4,820,749, teaches an aspen pulp polypropylene composite having about 40 wt % pulp and a modulus of less than 100,000. Dehennau et al., U.S. Pat. No. 5,164,432 and Bortoluzzi et al., U.S. Pat. No. 5,215,695, show sawdust containing composites with less than 50 wt % fiber and a modulus less than 800,000. Malucelli et al., EP Application No. 540026, teach a wood flour polypropylene composite having 50 wt % polymer and a modulus less than 700,000. In summary, the prior art relating to polypropylene composites typically uses 50 wt % or less fiber, exhibits a modulus of less than 800,000 and is not particularly descriptive regarding manufacturing process conditions or valuable thermal or structural properties. The industry has not succeeded in manufacturing a high strength and thermally stable composite. The industry has failed to prepare a complex thin-wall profile structural member from polypropylene and a reinforcing fiber that can show structural integrity over the life of a fenestration unit.
A substantial need exists for an improved polyolefin-wood fiber composite structural material that can be extruded into a weatherable, color stable, engineering structural member. Such a structural member requires physical stability, color stability, a controllable coefficient of thermal expansion and sufficient modulus to survive in a construction installation and while exposed to the exterior environment. The composite must be extruded or extrudable into a shape that is a direct substitute in assembly properties and structural properties for a wooden or extruded aluminum member. Such materials must be extrudable into reproducible, stable dimensions and useful cross-sections with a low heat transmission rate, improved resistance to insect attack, improved resistance to water absorption and rot resistance when in use combined with hardness and rigidity that permits sawing, milling and obtains fastening retention properties comparable to wood members and aluminum members. Accordingly, a substantial need exists for further developments in the manufacture of composite members for fenestration units.
We have found a substantially improved polyolefin wood fiber composite material that when extruded into structural members provide surprisingly improved mechanical properties including: tensile modulus, and mechanical stability (heat deflection) at elevated temperature. Applicants have unexpectedly discovered that xe2x80x9ccompatibilizationxe2x80x9d of acicular wood fibers having specified moisture content provides a melt rheology conducive to production of improved extruded, fiber reinforced structural members. A further feature of the invention resides in applicant""s recognition that the melt rheology permits use of extrusion tooling (dies, calibration blocks, etc.) designed for a poly(vinylchloride) (PVC) wood fiber composite material also known as FIBREX(copyright). Applicants believe that the superior mechanical properties of the structural members are due to improved wood fiber alignment and fiber-resin compatibilization (wetting).
The polypropylene composite combines about 5 to 50 parts of a polyolefin polyethylene or polypropylene with greater than about 50 to 90 parts of a wood fiber having an aspect ratio greater than about 2 and a fiber size that falls between about 50 microns and about 2000 microns. Preferably the fiber size ranges from about 100 to about 1000 microns and most preferably from about 100 to about 500 microns. The useful polyolefin material is a polyethylene or polypropylene polymer having a melting point of about 140 to 160xc2x0 C., preferably about 145 to 158xc2x0 C. The preferred polyethylene material is a polyethylene homopolymer or copolymer with 0.01 to 10 wt. % of a C2-16 olefin monomer. The preferred molecular weight (Mw) is about 10,000 to 60,000. The preferred polypropylene material is a polypropylene homopolymer or copolymer with 0.01 to 10 wt % of ethylene or a C4-16 olefin monomer or mixtures thereof. The preferred molecular weight (Mw) is about 10,000 to 60,000. The composite is also compatibilized using a compatibilizing agent that improves the wetting of the polymer on the fiber particle. In a preferred mode, the wood fiber is dried as thoroughly as possible. The useful fiber material is dried to a content of less than about 5000 parts, preferably less than 3500 parts of water per each million parts of wood fiber (ppm) resulting in an open cell wood fiber state in which the polypropylene polymer can then wet and penetrate the open cell fiber structure. The combination of these parameters in the composite results in a composite having surprisingly improved structural properties and thermal properties. The polypropylene-wood fiber composite was manufactured in two stages. In the first stage, polypropylene resin and wood fiber were fed into the compounder and pelletized. A vacuum was applied downstream to reduce the final moisture content. Also, another vacuum was applied in the transition box between the twin-screw compounder and the single-screw extruder to further reduce the moisture content and also to lower the temperature. These were called Precursor pellets. In the second stage, the precursor pellets and the compatibilizer were fed directly into the feed port and pelletized. The compounded and pelletized material from the second stage was called the Composite. Both, the biofiber and the resin were added simultaneously for two reasons. One, to minimize fiber degradation in the screw i.e., to maintain the fiber aspect ratio. The resin is allowed to coat the fiber and hence act as a lubricant. Two, incorporating the resin downstream into the hot fiber would result in lowering of temperature and increase the tendency of clumping leading to non-uniform distribution of the fiber within the matrix. In the second stage, the solid compatibilizers were added along with the precursor into the feed port in an initial zone. The liquid compatibilizers were added downstream into melt. Liquid compatibilizer experiments resulted in dark samples due to discoloration and excessive heat history and these were not pursued further. The two-stage process was also beneficial from a moisture control point of view. More than 95% of the initial moisture was removed in stage 1 of the process. This moisture removal is of utmost importance for increasing the effectiveness of the coupling agents being added in stage 2.
The general formulation parameters are as follows for the composite.
Preferred polypropylene is available in different forms including homopolymer, random copolymer and impact copolymers. The ethylene content in random copolymers varies from 2-5% and from 5-8% in impact copolymers. The ethylene portion is responsible for imparting the impact strength while the propylene portion imparts the rigidity. Typical properties of these two types of polymers are given in Table 2. Higher impact strength copolymers tend to lose some stiffness or rigidity. Montell polypropylene random copolymer SV-258 resin was identified and used as the base polymer for all experiments in this phase.
We have also developed a weatherable, mechanically stable, thin-walled complex, hollow profile material. The term xe2x80x9cthin-walledxe2x80x9d contemplates a profile having an open internal hollow structure. The structure is surrounded by a thin wall having a thickness dimension of about 1 to about 10 millimeters, preferably about 2 to 8 millimeters. Any internal support webs or fastener anchor locations have a wall thickness of about 5 to 8 mm. The profile is manufactured from a composite comprising an improved polypropylene polymer composition and wood fiber. The wood fiber is a specially prepared material having controlled moisture content, particle size and aspect ratio. The resulting structural member is extruded into a complex hollow profile having a defined support direction. The modulus of the profile is about 8xc2x7105 psi. The compressive strength of the profile in the defined support directions greater than about 1.2xc2x7103 psi. Such profiles can be assembled into a useful unit in institutional or residential real estate construction. The profiles can be joined using a variety of adhesive and welding joining techniques for forming a secure joint between profile members. The modulus of the profile is about 5.5 gigapascals. The compressive strength of the profile in the defined support directions is greater than about 8.8 gigapascals. The profile, can optionally include a weatherable capstock material that has a stable color and appearance defined as less than a Delta E value of less than two 2 Hunter Lab units upon 60 months of accelerated weathering as determined by ASTM D2244 Section 6.3 (after exposure per Section 7.9.1.1). Such profiles can be assembled into a useful unit in institutional or residential real estate construction. The profiles can be joined using a variety of adhesive and welding joining techniques for forming a secure joint between profile members. The profile can have a capstock layer with a thickness of about 0.05 to 1 mm, preferably about 0.1 to 0.5 millimeters coextruded on any visible exterior portion or the entire exterior portion of the profile. The capstock can cover greater than 20% of the exterior area, 20 to 80% of the exterior area or virtually 100% of the exterior area, depending on the application of the profile. The profile can have a capstock layer with a thickness of about 0.05 to 1 mm, preferably about 0.1 to 0.5 millimeters coextruded on any visible exterior portion or the entire exterior portion of the profile. The capstock can cover greater than 20% of the exterior area, 20 to 80% of the exterior area or virtually 100% of the exterior area, depending on the application of the profile.
For the purpose of the patent application, the term xe2x80x9caspect ratioxe2x80x9d indicates an index number obtained by dividing the length of the fiber by its width. Molecular weights disclosed in this patent application are weight average molecular weights (Mw). The physical parameters of the materials made in this application are measured using ASTM methods which are disclosed throughout the application. The term complex profile is intended to mean an extruded thermoplastic article having a hollow internal structure. Such structure includes a complex exterior surface geometry or structure, at least one support web providing mechanical stability in a defined support direction. Alternatively the complex profile structure can comprise one, or more fastener anchor means or locations to improve assembly or installation. The term defined support direction is intended to mean a direction of force or a line of strain opposing the force derived from the environment. Examples of such force includes the force of a step upon a threshold, the force of closing a sash, the force of gravity, wind load forces and forces rising from the anisotropic stress resulting from the non-planar installation of the unit.